LG Electronics GSA-4168B, GSA-4165B, GSA-4167B service manual Focus Circuit, Focus Servo

2. Focus Circuit

2-1. Block Diagram

			A+B+C+D
							HAVC
					LPF	G	LS	3	PE
		A,B,C,D					to
							0.8V
					IC101
					R2S35002		HAVC
		A,B,C,D
					LPF	G	LS	2
							to
	(EF1~EF4)							FE	FE
							V14
Disc	Optical		(A+C)-(B+D)						R102
Motor unit	Pick-up		(A+C)-(B+D)+K[(EF1+EF3)-(EF2+EF4)]						C405
	HOP-7632TS
			FOD						FE	R103
						Focusing
				180	DAC		ADC	169	GND
						Compensator				C406
	FACT- FACT+				IC301			170
					R8J32007				PE
										GND
	FACT+	34		40	FOIN			R329	FOD
	FACT-	35			REF			C335
			IC601	42					1.65V
		R2S30202FP			EN1
				20		CTL1
				21	EN2	CTL2

2-2. Focus Servo

The aim of Focus Servo is to maintain the distance between object lens of P/U and disc surface, so that the detected RF signal(A, B, C, D, EF1, EF2, EF3, EF4) can be maximized.

Focus Error Signal(FE) generates from focus error detection block in RF IC(R2S35002) using Conventional Astigmatism Detection method, Differential Astigmatism Detection method.

Focus Gain and path can be changed at the RF IC(R2S35002) according to the disc, and the resulting output FE(R2S35002 2pin) is input to DSP IC(R2S35002 169pin).

The Focus Search operation is using FE, PE Signal, therefore check FE, PE signals when Focusing is failed.

The role of DSP IC(R8J32007) is Focus Digital Controller. The operation path is as follows;

FE Signal is input to DSP IC(R8J32007 169pin), and after A/D Conversion, Digital Equalizer Block and D/A Conversion in R8J32006FP, the output signal FOD(R8J32007 180pin) is input to Drive IC(R2S30202FP 40pin). The drive output signal FACT+/FACT- generated according FOIN(R2S30202FP 40pin), and drives focus actuator in the P/U unit.

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